The present invention relates generally to electronic devices whose functional length scales are measured in nanometers, and, more particularly, to simple devices used as building blocks to form more complicated structures, and to the methods for forming such devices. Devices both of micrometer and nanometer scale may be constructed in accordance with the teachings herein.
The area of molecular electronics is in its infancy. To date, there has been only one convincing demonstration of a molecule acting as an electronic switch published in the open literature (see, C. P. Collier et al., Science, Vol. 285, pp. 391-394 (Jul. 16, 1999)), but there has been a great deal of speculation and interest within the scientific community surrounding this topic since the mid-1970s. In the published work, a monolayer film of molecules called rotaxanes were trapped between two metal electrodes and caused to switch from an ON state to an OFF state by the application of a positive bias voltage across the molecules. The ON and OFF states differed in resistivity by about a factor of 100 because of a change in the rate of tunneling through the molecules caused by oxidizing the molecules with an applied voltage.
The primary problem with the rotaxanes was that this example was an irreversible switch. It can only be toggled once. Thus, it can be used in a programmable read-only memory (PROM), but not in a ROM-like device nor in a reconfigurable system, such as a defect-tolerant communications and logic network. Rotaxanes require an oxidation and/or reduction reaction to occur before the switch can be toggled. This requires the expenditure of a significant amount of energy to toggle the switch. In addition, the large and complex nature of rotaxane molecules and related compounds potentially makes the switching times of the molecules slow.
Thus, there remains a need for a molecular species that has two stable states, which permit reversible switching from one state to the other. Such a bistable molecule must evidence rapid switching times to be of use in micro-scale and nanoscale devices.
In accordance with the present invention, nanometer-scale reversible electronic switches are provided that can be assembled to make cross-bar circuits that provide memory, logic, and communications functions. The electronic switches, or crossed-wire devices, comprise a pair of crossed wires that form a junction where one wire crosses another at an angle other than zero degrees and at least one connector species connecting the pair of crossed wires in the junction The junction has a functional dimension in nanometers. The connector species comprises a bistable molecule having a general formula given by 
where the letters in Formula (I) are defined as follows:
A=CH; N; C-alkyl; C-halogen; Cxe2x80x94OH; Cxe2x80x94OR(ether); Cxe2x80x94SR(thioether); C-amide; C-ester or thioester;
B=CH; N; C-alkyl; C-halogen; ; Cxe2x80x94OH; Cxe2x80x94OR(ether); Cxe2x80x94SR(thioether); C-amide; C-ester or thioester;
D=CH; N; C-alkyl; C-halogen; Cxe2x80x94OH; Cxe2x80x94OR(ether); Cxe2x80x94SR(thioether); C-amide; C-ester or thioester;
E=CH; N; C-alkyl; C-halogen; Cxe2x80x94OH; Cxe2x80x94OR(ether); Cxe2x80x94SR(thioether); C-amide; C-ester or thioester;
F=CH; N; C-alkyl; C-halogen; Cxe2x80x94OH; Cxe2x80x94OR(ether); Cxe2x80x94SR(thioether); C-amide; C-ester or thioester;
G=CH; N; C-alkyl; C-halogen; Cxe2x80x94OH; Cxe2x80x94OR(ether); Cxe2x80x94SR(thioether); C-amide; C-ester or thioester;
J=CH; N; C-alkyl; C-halogen; Cxe2x80x94OH; Cxe2x80x94OR(ether); Cxe2x80x94SR(thioether); C-amide; C-ester or thioester;
K=CH; N; C-alkyl; C-halogen; Cxe2x80x94OH; Cxe2x80x94OR(ether); Cxe2x80x94SR(thioether); C-amide; C-ester or thioester;
M=CH2; CF2; CCl2; CHOCH3; CHOH; CHF; CO; CHxe2x95x90CH; CH2xe2x80x94CH2; S; O; NH; NR; NCOR; or NCOAr;
Q=CH; nitrogen; phosphorus; or boron;
Y=O or S; and
Z=R (H; alkyl); NHR; OR; SR; CHR-NHR; CHRxe2x80x94OR; CHRxe2x80x94SR; CHRxe2x80x94X (halogen); NRxe2x80x94NHR; NRxe2x80x94OR; or NRxe2x80x94SR.
The bistable molecules evidence high switching speed. Such molecules are essentially stable against switching due to thermal fluctuations.